Actually, CattivaGattina, the gal who wrote it has lupus; but I found it when my diagnosis was fibromyalgia, and it was very popular in fibro circles. My base dx is Ehlers Danlos Syndrome, hypermobility type. The pain is very similar to fibro, and I have the added joys of dislocating joints.
All y'all, I really recommend reading Spoon Theory, which you can find, here:
You very likely know someone with some sort of invisible illness or invisible disability. This is a very useful tool for understanding them, or even the young person you see driving a car with a handicapped plate, or healthy-appearing person who's sitting at the front of the bus.
It's hard to explain the beauty and usefulness of spoon theory; it's much simpler to read the original. It moved me to tears when I read, because it was created by a young woman who just wanted to have a normal life. She was having a girl's-night-out with her bestie, and her bestie inquired about her condition. She spontaneously came up with spoon theory to explain it.
After all that, I will add that I don't see it very applicable to poly. Though I'm glad you've found a way to explain things that works for you.
I do think lots of people need encouragement, and tips, and ideas, (and maybe some need symbolism), on how to begin and continue communicating effectively. Lots and lots of us didn't have even remotely close to good modeling for how to do this.